In the past, various different techniques have been used in an attempt to flow air through a contained space of a system including air distribution systems for conditioning the temperature of the air with the rate of such air flow being related to the static pressure in the system. The rate of air flow (CFM-cubic feet per minute) through the air distribution system also affects the speed and torque of a motor used in the system.
One approach of the past involved the laborious task of matching the motor speed and torque with the proper fan to approximate the desired air flow rate for the particular contained space and static pressure of the particular air distribution system. However, this did not accommodate variations in the static pressure in the air distribution system caused by alterations in the system such as opening, closing or adjusting of a damper connecting a conditioned space in air flow relation with the system. In addition, other devices, such as filter and heat exchangers, may alter the static pressure within the duct system.
If the fan or blower utilized in such prior art systems was of the fan or blade type, an increase in the static pressure acting on such fan resulted in decrease in the air flow rate.
Another prior art approach has been to compensate for the alteration in the speed of fans and the electric motors by employing an apparatus for controlling the motor speed which required the calculation of constants specific for each apparatus and air distribution system combination. This apparatus was included in a controller which drives the motor at various speed but was in case of a synchronous motor and actual motor speed is equal to supplied frequency from an inverter to a motor. If an induction motor and AC inverter controller are used, actual motor speed is different from supplied frequency and a slip that is difference in speed between actual motor speed and supplied frequency depends on resistance to have to be taken into account.
It is an object of the present invention to provide an improved system for conditioning air and for maintaining a pre-selected airflow rate of conditioned air through at least part of the system regardless of the static pressure therein.
It is a further object of the present invention to provide an improved airflow control system, which can be utilised in conjunction with numerous duct systems without the need for calibration particular to the specific duct system.
It is another object of the present invention to provide an improved method, which directly calculates the actual airflow of the air distribution system.
It is yet another object of the present invention to provide an improved method for applying to a combination of induction motor and AC inverter controller which is cheaper than a combination of synchronous motor and DC inverter controller.